The present invention relates generally to the control of electrical circuits such as relays. More particularly, the invention relates to a technique for avoiding the ill effects of leakage current in circuits designed to switch on and off coils or other operators for such devices.
Many applications exist for remote switching devices such as relays. In general, such devices typically include one or more contacts which can be opened or closed in response to energization of a coil. Both electromechanical and solid state relays are commonly available. Sizes and ratings of such devices vary widely, depending upon the needs of particular applications, and upon such factors as whether the relays power significant loads or simply provide low-level feedback. Families of relays are currently available which are quite small in physical packaging, and which can be mounted on circuit boards, and other relatively small supports.
A difficulty in application and reliability of certain relays resides in the presence of leakage current in circuitry used to energize the relay coil. In certain relays, particularly in smaller size relays such as those mountable on circuit boards and other small support structures, even low levels of leakage current can cause the relay coil to be energized when such energization is not desired, thereby causing the relay to open or close in an undesirable fashion. Similarly, such leakage current can cause the coil to remain energized a sufficient degree to prevent shifting of the contact or contacts upon removal of a control signal to the coil. In either case, the reliability of the relay and the signals produced by the relay is jeopardized by the leakage current.
There is a need, therefore, for an improved technique for controlling relays and similar circuits. There is a particular need for circuitry which can more reliably switch on and off a relay coil. There is, at present, a need for relatively straightforward and simple circuitry which can suppress leakage current in relay circuits so as to improve their reliability.